ipc/ipc_sync_channel.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef IPC_IPC_SYNC_CHANNEL_H_
   6 #define IPC_IPC_SYNC_CHANNEL_H_
   7
   8 #include <string>
   9 #include <deque>
  10
  11 #include "base/basictypes.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "base/synchronization/lock.h"
  14 #include "base/synchronization/waitable_event_watcher.h"
  15 #include "ipc/ipc_channel_handle.h"
  16 #include "ipc/ipc_channel_proxy.h"
  17 #include "ipc/ipc_sync_message.h"
  18
  19 namespace base {
  20 class WaitableEvent;
  21 };
  22
  23 namespace IPC {
  24
  25 class SyncMessage;
  26
  27 // This is similar to ChannelProxy, with the added feature of supporting sending
  28 // synchronous messages.
  29 //
  30 // Overview of how the sync channel works
  31 // --------------------------------------
  32 // When the sending thread sends a synchronous message, we create a bunch
  33 // of tracking info (created in Send, stored in the PendingSyncMsg
  34 // structure) associated with the message that we identify by the unique
  35 // "MessageId" on the SyncMessage. Among the things we save is the
  36 // "Deserializer" which is provided by the sync message. This object is in
  37 // charge of reading the parameters from the reply message and putting them in
  38 // the output variables provided by its caller.
  39 //
  40 // The info gets stashed in a queue since we could have a nested stack of sync
  41 // messages (each side could send sync messages in response to sync messages,
  42 // so it works like calling a function). The message is sent to the I/O thread
  43 // for dispatch and the original thread blocks waiting for the reply.
  44 //
  45 // SyncContext maintains the queue in a threadsafe way and listens for replies
  46 // on the I/O thread. When a reply comes in that matches one of the messages
  47 // it's looking for (using the unique message ID), it will execute the
  48 // deserializer stashed from before, and unblock the original thread.
  49 //
  50 //
  51 // Significant complexity results from the fact that messages are still coming
  52 // in while the original thread is blocked. Normal async messages are queued
  53 // and dispatched after the blocking call is complete. Sync messages must
  54 // be dispatched in a reentrant manner to avoid deadlock.
  55 //
  56 //
  57 // Note that care must be taken that the lifetime of the ipc_thread argument
  58 // is more than this object.  If the message loop goes away while this object
  59 // is running and it's used to send a message, then it will use the invalid
  60 // message loop pointer to proxy it to the ipc thread.
  61 class IPC_EXPORT SyncChannel : public ChannelProxy {
  62  public:
  63   enum RestrictDispatchGroup {
  64     kRestrictDispatchGroup_None = 0,
  65   };
  66
  67   // Creates and initializes a sync channel. If create_pipe_now is specified,
  68   // the channel will be initialized synchronously.
  69   // The naming pattern follows IPC::Channel.
  70   static scoped_ptr<SyncChannel> Create(
  71       const IPC::ChannelHandle& channel_handle,
  72       IPC::Channel::Mode mode,
  73       Listener* listener,
  74       base::SingleThreadTaskRunner* ipc_task_runner,
  75       bool create_pipe_now,
  76       base::WaitableEvent* shutdown_event);
  77
  78   // Creates an uninitialized sync channel. Call ChannelProxy::Init to
  79   // initialize the channel. This two-step setup allows message filters to be
  80   // added before any messages are sent or received.
  81   static scoped_ptr<SyncChannel> Create(
  82       Listener* listener,
  83       base::SingleThreadTaskRunner* ipc_task_runner,
  84       base::WaitableEvent* shutdown_event);
  85
  86   virtual ~SyncChannel();
  87
  88   virtual bool Send(Message* message) OVERRIDE;
  89
  90   // Sets the dispatch group for this channel, to only allow re-entrant dispatch
  91   // of messages to other channels in the same group.
  92   //
  93   // Normally, any unblocking message coming from any channel can be dispatched
  94   // when any (possibly other) channel is blocked on sending a message. This is
  95   // needed in some cases to unblock certain loops (e.g. necessary when some
  96   // processes share a window hierarchy), but may cause re-entrancy issues in
  97   // some cases where such loops are not possible. This flags allows the tagging
  98   // of some particular channels to only re-enter in known correct cases.
  99   //
 100   // Incoming messages on channels belonging to a group that is not
 101   // kRestrictDispatchGroup_None will only be dispatched while a sync message is
 102   // being sent on a channel of the *same* group.
 103   // Incoming messages belonging to the kRestrictDispatchGroup_None group (the
 104   // default) will be dispatched in any case.
 105   void SetRestrictDispatchChannelGroup(int group);
 106
 107  protected:
 108   class ReceivedSyncMsgQueue;
 109   friend class ReceivedSyncMsgQueue;
 110
 111   // SyncContext holds the per object data for SyncChannel, so that SyncChannel
 112   // can be deleted while it's being used in a different thread.  See
 113   // ChannelProxy::Context for more information.
 114   class SyncContext : public Context {
 115    public:
 116     SyncContext(Listener* listener,
 117                 base::SingleThreadTaskRunner* ipc_task_runner,
 118                 base::WaitableEvent* shutdown_event);
 119
 120     // Adds information about an outgoing sync message to the context so that
 121     // we know how to deserialize the reply.
 122     void Push(SyncMessage* sync_msg);
 123
 124     // Cleanly remove the top deserializer (and throw it away).  Returns the
 125     // result of the Send call for that message.
 126     bool Pop();
 127
 128     // Returns an event that's set when the send is complete, timed out or the
 129     // process shut down.
 130     base::WaitableEvent* GetSendDoneEvent();
 131
 132     // Returns an event that's set when an incoming message that's not the reply
 133     // needs to get dispatched (by calling SyncContext::DispatchMessages).
 134     base::WaitableEvent* GetDispatchEvent();
 135
 136     void DispatchMessages();
 137
 138     // Checks if the given message is blocking the listener thread because of a
 139     // synchronous send.  If it is, the thread is unblocked and true is
 140     // returned. Otherwise the function returns false.
 141     bool TryToUnblockListener(const Message* msg);
 142
 143     // Called on the IPC thread when a sync send that runs a nested message loop
 144     // times out.
 145     void OnSendTimeout(int message_id);
 146
 147     base::WaitableEvent* shutdown_event() { return shutdown_event_; }
 148
 149     ReceivedSyncMsgQueue* received_sync_msgs() {
 150       return received_sync_msgs_.get();
 151     }
 152
 153     void set_restrict_dispatch_group(int group) {
 154       restrict_dispatch_group_ = group;
 155     }
 156
 157     int restrict_dispatch_group() const {
 158       return restrict_dispatch_group_;
 159     }
 160
 161     base::WaitableEventWatcher::EventCallback MakeWaitableEventCallback();
 162
 163    private:
 164     virtual ~SyncContext();
 165     // ChannelProxy methods that we override.
 166
 167     // Called on the listener thread.
 168     virtual void Clear() OVERRIDE;
 169
 170     // Called on the IPC thread.
 171     virtual bool OnMessageReceived(const Message& msg) OVERRIDE;
 172     virtual void OnChannelError() OVERRIDE;
 173     virtual void OnChannelOpened() OVERRIDE;
 174     virtual void OnChannelClosed() OVERRIDE;
 175
 176     // Cancels all pending Send calls.
 177     void CancelPendingSends();
 178
 179     void OnWaitableEventSignaled(base::WaitableEvent* event);
 180
 181     typedef std::deque<PendingSyncMsg> PendingSyncMessageQueue;
 182     PendingSyncMessageQueue deserializers_;
 183     base::Lock deserializers_lock_;
 184
 185     scoped_refptr<ReceivedSyncMsgQueue> received_sync_msgs_;
 186
 187     base::WaitableEvent* shutdown_event_;
 188     base::WaitableEventWatcher shutdown_watcher_;
 189     base::WaitableEventWatcher::EventCallback shutdown_watcher_callback_;
 190     int restrict_dispatch_group_;
 191   };
 192
 193  private:
 194   SyncChannel(Listener* listener,
 195               base::SingleThreadTaskRunner* ipc_task_runner,
 196               base::WaitableEvent* shutdown_event);
 197
 198   void OnWaitableEventSignaled(base::WaitableEvent* arg);
 199
 200   SyncContext* sync_context() {
 201     return reinterpret_cast<SyncContext*>(context());
 202   }
 203
 204   // Both these functions wait for a reply, timeout or process shutdown.  The
 205   // latter one also runs a nested message loop in the meantime.
 206   static void WaitForReply(
 207       SyncContext* context, base::WaitableEvent* pump_messages_event);
 208
 209   // Runs a nested message loop until a reply arrives, times out, or the process
 210   // shuts down.
 211   static void WaitForReplyWithNestedMessageLoop(SyncContext* context);
 212
 213   // Starts the dispatch watcher.
 214   void StartWatching();
 215
 216   // Used to signal events between the IPC and listener threads.
 217   base::WaitableEventWatcher dispatch_watcher_;
 218   base::WaitableEventWatcher::EventCallback dispatch_watcher_callback_;
 219
 220   DISALLOW_COPY_AND_ASSIGN(SyncChannel);
 221 };
 222
 223 }  // namespace IPC
 224
 225 #endif  // IPC_IPC_SYNC_CHANNEL_H_